Climate: How stable is the East Antarctica ice sheet?

New research suggests significant melting during Pliocene era, when CO2 levels and temps were comparable to levels projected by 2100

Parts of the Antarctic ice sheets may not be as stable in the face of climate change as previously believed. Bob Berwyn photo.

By Summit Voice

FRISCO — The biggest ice sheet in the world may be more susceptible to a warming climate than previously believed.

New evidence garnered from mud deposits suggests that the East Antarctica Ice Sheet may have experiences significant melting about 5 million years ago — enough to raise sea level by about 60 feet worldwide, according to researchers from Imperial College London.

The study, published last week in the journal Nature Geoscience, shows that there was repeated melting between five and three million years ago, during a geological period called Pliocene Epoch, when atmospheric CO2 levels were similar to today’s and temperatures comparable to what’s being projected by the end of this century.

“Our study underlines that these conditions have led to a large loss of ice and significant rises in global sea level in the past,” said Dr Tina Van De Flierdt, co-author from the Department of Earth Science and Engineering at Imperial College London.

“Scientists predict that global temperatures of a similar level may be reached by the end of this century, so it is very important for us to understand what the possible consequences might be,” Van De Flierdt said.

Most scientists believe the East Antarctic Ice Sheet — about the size of Australia — stabilized in size about 14 million years ago, but the new research suggests that the ice sheet had partially melted during this “stable” period.

The clues came from the chemistry of muddy sea-bottom sediments drilled from more than three kilometres below sea level off the coast of Antarctica.

Analyzing the mud revealed a chemical fingerprint that enabled the team to trace where it came from on the continent. They discovered that the mud originated from rocks that are currently hidden under the ice sheet. The only way that significant amounts of this mud could have been deposited as sediment in the sea would be if the ice sheet had retreated inland and eroded these rocks, according to the team.

The melting of the ice sheet may have been caused in part by the fact that some of it rests in basins below sea level. This puts the ice in direct contact with seawater and when the ocean warms, as it did during the Pliocene, the ice sheet becomes vulnerable to melting.

“Scientists previously considered the East Antarctic ice sheet to be more stable than the much smaller ice sheets in West Antarctica and Greenland, even though very few studies of East Antarctic ice sheet have been carried out,” said Carys Cook, co-author and research postgraduate from the Grantham Institute for Climate Change.

“Our work now shows that the East Antarctic ice sheet has been much more sensitive to climate change in the past than previously realized. This finding is important for our understanding of what may happen to the Earth if we do not tackle the effects of climate change.”

Next, the team will analyze sediment samples to determine how quickly the East Antarctic ice sheet melted during the Pliocene. This information could be useful in the future for predicting how quickly the ice sheet could melt as a result of global warming.